Project 1 "Novel inflammatory responses of injured endothelium." Acute respiratory Distress Syndrome (ARDS) is a frequent syndrome with a mortality that remains high even 30 years after its initial description. A leading cause of ARDS is bacteremia and sepsis, accounting for a third of those diagnosed with ARDS, and about a third of those with sepsis syndrome will display the clinical features that lead to a diagnosis of ARDS. The outer leaflet of gram bacteria is comprised of lipopolysaccharide (LPS), and this is a potent pleotropic inflammatory mediator in vivo and in vitro. LPS injection recapitulates many of the manifestations of sepsis, and LPS inhalation approximates early features of ARDS. In contrast to models of LPS-endotoxemia, the results of therapeutic strategies based on blocking LPS have not been as encouraging in clinical trials of human sepsis and its consequences, including ARDS. While several valid reasons exist for the differences between LPS-induced endotoxemia versus clinical sepsis, one difference is that pathogenic bacteria elaborate more than a single agent that can activate cellular responses, dysregulate inflammatory cell-cell interactions, and open the doors to sepsis syndrome. A clinical observation that clearly supports this possibility is that ARDS is "triggered" by gram+ bacteria that do not contain LPS, an event growing relevance as sepsis syndrome caused by gram+ bacteria may be increasing. Thus, there is more to sepsis than LPS. This proposal is predicated on our observation that two proteins with an N-terminal modification that is common among gram-, gram+, and even intracellular pathogens behave in some ways like LPS. This is clearly documented in our in vitro and in vivo preliminary studies. Success in elucidating the chemical structure of LPS has allowed LPS to become synonymous with the more general term endotoxin, and this has overshadowed older literature describing endotoxin proteins. We propose that a common lipid modification of bacterial proteins confers endotoxic properties to the nearly forgotten class of endotoxic proteins. The relative role of LPS and certain bacterial proteins as endotoxins is further confused by the contamination of LPS preparations with the more potent endotoxic proteins. The Aims are designed to clarify the overlapping activities, and to determine if, and how, the triacylCys modification is pro-inflammatory.